1. Field of the Invention
The present invention relates to dye sensitized solar cells, and in particular relates to the method for manufacturing the electrode thereof.
2. Description of the Related Art
Solar photocells are photoelectric semiconductor thin films directly powered by the solar light, and it immediately outputs voltage and current by exposed light. The solar photocell is usually called solar cell for short. The solar cell is a renewable green energy without producing harmful gas such as carbon dioxide during generating power, and it will not pollute the environment. The solar cells are classified to silicon-based semiconductor cell, dye sensitized solar cell, organic cell, and the likes corresponding to the materials. The most important factor of the solar cell is the photoelectric conversion yield. In the silicon based solar cells, the best conversion yields of the single crystalline silicon solar cell, the multi crystalline silicon solar cell, and the amorphous silicon solar cell are 29%, 24%, and 17%, respectively.
The dye sensitized solar cell (in abbreviate DSSC) is recently developed. Different from the typical photovoltage cell, the top substrate of the DSSC is usually glass or transparent flexible polymer foil. The glass has a transparent conductive oxide coated thereon, such as fluorinated tin oxide (SnO2:F, in abbreviate FTO) or indium tin oxide (in abbreviate ITO). There is a nano-porous layer having a thickness of about 10 μm formed on the transparent conductive layer, wherein the nano-porous layer is generally composed of TiO2 particles having a particle size diameter of about 10 nm to 20 nm. Subsequently, a dye layer such as ruthenium polypyridyl complex is coated on the nano-porous layer to complete so-called top substrate. The bottom substrate is usually glass or transparent flexible polymer foil, wherein the glass has a transparent conductive oxide layer such as FTO coated thereon. Furthermore, a platinum layer is plated on the transparent conductive layer to be the catalyst for the electrolyte reaction. An electrolyte containing iodonium is then injected to the space between the top and bottom substrates. Although the best conversion yield of the DSSC is only about 12%, the manufacture of the DSSC is simple and thereby largely reducing the mass production cost and the price of per kilowatt-hour.
U.S. Pat. No. 6,881,604 discloses a method of wet coating collocated with compression to prepare photoelectric electrode applied in the DSSC, but its conversion yield is only 3% under light intensity of 100 mW/cm2.
Chem. Commun., 2007, 4767-4769 discloses that the TiO2 of different particle size diameters is wet coated to form a TiO2 film on ITO/PEN, and the TiO2 film is then compressed by 100 MPa to enhance the linkage of the TiO2 particles, thereby completing a working electrode. The best conversion yield of the DSSC including this working electrode may reach 7.4%, wherein the active area is 0.256 cm2.
CN 1763261 discloses the TiO2 being electrophoresis deposited on a cathode by appling a constant voltage, wherein the electrophoresis solution must include surfactant and metal salt. Thereafter, the electrode has to be treated by high temperature or microwave. However, the TiO2 layer only has single particle size diameter distribution and needs to be dipped in the dye solution.
The conventional low temperature processes for preparing the electrode still exist some defects. For example, the slurry containing binder needs high temperature sintering to remove the organic, such that the slurry cannot be utilized in thermal stabless flexible substrates. Accordingly, the low temperature wet coating should additionally prepare complex slurry to avoid sintering process. As such, a novel method for manufacturing the electrode applied in solar cell is called for reducing the process time and cost.